In recent years, an adaptive array radio base station employing an array antenna is put into practice as a radio base station for a mobile communication system such as a portable telephone. The operation principle of such an adaptive array radio base station is described in the following literature, for example:
B. Widrow, et al.: “Adaptive Antenna Systems”, Proc. IEEE, vol. 55, No. 12, pp. 2143–2159 (December 1967).
S. P. Applebaum: “Adaptive Arrays”, IEEE Trans. Antennas & Propag., vol. AP-24, No. 5, pp. 585–598 (September 1976).
O. L. Frost, III: “Adaptive Least Squares Optimization Subject to Linear Equality Constraints”, SEL-70-055, Technical Report, No. 6796-2, Information System Lab., Stanford Univ. (August 1970).
B. Widrow and S. D. Stearns: “Adaptive Signal Processing”, Prentice-Hall, Englewood Cliffs (1985).
R. A. Monzingo and T. W. Miller: “Introduction to Adaptive Arrays,” John Wiley & Sons, New York (1980).
J. E. Hudson: “Adaptive Array Principles”, Peter Peregrinus Ltd., London (1981).
R. T. Compton, Jr.: “Adaptive Antennas—Concepts and Performance”, Prentice-Hall, Englewood Cliffs (1988).
E. Nicolau and D. Zaharia: “Adaptive Arrays”, Elsevier, Amsterdam (1989).
FIG. 16 is a model diagram conceptually showing the operation principle of such an adaptive array radio base station. Referring to FIG. 16, one adaptive array radio base station 1 comprises an array antenna 2 having n antennas #1, #2, #3, . . . , #n, and the range where its radio waves reach is expressed as a first oblique line area 3. On the other hand, the range where radio waves of another adjacent radio base station 6 reach is expressed as a second oblique line area 7.
In the area 3, transmission/receiving of radio signals is performed between a portable telephone 4 which is the terminal of a user A and the adaptive array radio base station 1 (arrow 5). In the area 7, on the other hand, transmission/receiving of radio signals is performed between a portable telephone 8 which is the terminal of another user B and the radio base station 6 (arrow 9).
When the frequency of the radio signal of the portable telephone 4 of the user A and the frequency of the radio signal of the portable telephone 8 of the user B happen to be equal to each other, it follows that the radio signal from the portable telephone 8 of the user B becomes an unnecessary interference signal in the area 3 and mixes into the radio signal between the portable telephone 4 of the user A and the adaptive array radio base station 1.
Thus, the adaptive array radio base station 1 receiving the mixed radio signals from both of the users A and B comes to output a signal mixed with the signals from both of the users A and B unless performing some processing, and it follows that talking of the user A to originally make a call is hindered.
In order to remove this signal from the user B from the output signal, the adaptive array radio base station 1 performs the following processing: FIG. 17 is a schematic block diagram showing the structure of the adaptive array radio base station 1.
Assuming that the signal from the user A is A(t) and the signal from the user B is B(t), a receive signal x1(t) in the first antenna #1 forming the array antenna 2 of FIG. 16 is expressed in the following equation:x1(t)=a1×A(t)+b1×B(t)
At this point, a1 and b1 are coefficients changing in real time as described later.
Then, a receive signal x2(t) in the second antenna #2 is expressed in the following equation:x2(t)=a2×A(t)+b2×B(t)
At this point, a2 and b2 are also coefficients similarly changing in real time.
Then, a receive signal x3(t) in the third antenna #3 is expressed in the following equation:x3(t)=a3×A(t)+b3×B(t)
At this point, a3 and b3 are also coefficients similarly changing in real time.
Similarly, a receive signal xn(t) in the n-th antenna #n is expressed in the following equation:xn(t)=an×A(t)+bn×B(t)
At this pinot, an and bn are also coefficients similarly changing in real time.
The aforementioned coefficients a1, a2, a3, . . . , an express that difference takes place in receiving intensity in each antenna since relative positions of the respective ones of the antennas #1, #2, #3, . . . , #n forming the array antenna 2 are different with respect to the radio signal from the user A (for example, the respective antennas are arranged at intervals of about five times the wavelength of the radio signal, i.e., about 1 meter from each other).
The aforementioned coefficients b1, b2, b3, . . . , bn also express that difference takes place in receiving intensity in each of the antennas #1, #2, #3, . . . , #n with respect to the radio signal from the user B. Each user moves and hence these coefficients change in real time.
The signals x1(t), x2(t), x3(t), . . . , xn(t) enter a receiving part 1R forming the adaptive array radio base station 1 through corresponding switches 10-1, 10-2, 10-3, . . . , 10-n, and the signals are supplied to a weight vector control part 11, and also supplied to one inputs of corresponding multipliers 12-1, 12-2, 12-3, . . . , 12-n respectively.
Weights w1, w2, w3, . . . , wn for the receive signals in the respective antennas are applied to other inputs of these multipliers from the weight vector control part 11. Theses weights are calculated by the weight vector control part 11 in real time, as described later.
Therefore, the receive signal x1(t) in the antenna #1 becomes w1×(a1A(t)+b1B(t)) through the multiplier 12-1, the receive signal x2(t) in the antenna #2 becomes w2×(a2A(t)+b2B(t)) through the multiplier 12-2, the receive signal x3(t) in the antenna #3 becomes w3×(a3A(t)+b3B(t)) through the multiplier 12-3, and the receive signal xn(t) in the antenna #n becomes wn×(anA(t)+bnB(t)) through the multiplier 12-n. 
Outputs from these multipliers 12-1, 1-2, 12-3, . . . , 12-n are added by an adder 13, and its output becomes as follows:                w1(a1A(t)+b1B(t))+w2(a2A(t)+b2B(t))+w3(a3A(t)+b3B(t))+ . . . +wn(anA(t)+bnB(t))        
When dividing this to a term related to the signal A(t) and a term related to the signal B(t), it becomes as follows:                (w1a1+w2a2+w3a3+ . . . +wnan)A(t)+(w1b1+w2b2+w3b3+ . . . +wnbn)B(t)        
At this point, the adaptive array radio base station 1 calculates the aforementioned weights w1, w2, w3, . . . , wn to be capable of identifying the user A and B and extracting only the signal from the desired user, as described later. In the example of FIG. 17, for example, the weight vector control part 11 regards the coefficients a1, a2, a3, . . . , an, b1, b2, b3, . . . , bn as constants and calculates the weights w1, w2, w3, . . . , wn so that the coefficients of the signal A(t) become 1 as a whole and the coefficients of the signal B(t) become 0 as a whole, in order to extract only the signal A(t) from the user A to originally make a call.
In other words, the weight vector control part 11 calculates such weights w1, w2, w3, . . . , wn that the coefficients of the signal A(t) become 1 and the coefficients of the signal B(t) become 0 in real time by solving the following simultaneous linear equations:w1a1+w2a2+w3a3+ . . . +wnan=1w1b1+w2b2+w3b3+ . . . +wnbn=0
While description of a method of solving these simultaneous linear equations is omitted, it is well known as described in the literature listed above, and actually already put into practice in adaptive array radio base stations.
By thus setting the weights w1, w2, w3, . . . , wn, an output signal from the adder 13 becomes as follows:Output signal=1×A(t)+0×B(t)=A(t)
The aforementioned identification of the users A and B is performed as follows: FIG. 18 is a schematic diagram showing the frame structure of a radio signal of a portable telephone. The radio signal of the portable telephone is roughly formed by a preamble consisting of a signal series known to the radio base station and data (voice etc.) consisting of a signal series unknown to the radio base station.
The signal series of the preamble includes a signal series of information for judging whether or not this user is a desired user to make a call for the radio base station. The weight vector control part 11 (FIG. 17) of the adaptive array radio base station 1 compares a training signal corresponding to the user A extracted from a memory 14 and the received signal series with each other and performs weight vector control (decision of weights) to extract a signal conceivably including a signal series corresponding to the user A. The signal of the user A extracted in such a manner is externally output from the adaptive array radio base station 1 as an output signal SRX(t).
In FIG. 17, on the other hand, an external input signal STX(t) enters a transmission part 1T forming the adaptive array radio base station 1, and is supplied to single inputs of multipliers 15-1, 15-2, 15-3, . . . , 15-n. The weights w1, w2, w3, . . . , wn previously calculated by the weight vector control part 11 on the basis of the receive signals are copied and applied to other inputs of these multipliers respectively.
The input signal weighted by these multipliers is sent to the corresponding antennas #1, #2, #3, . . . , #n through the corresponding switches 10-1, 10-2, 10-3, . . . , 10-n and transmitted into the area 3 of FIG. 16.
At this point, weighting targeting the user A is performed on the signal transmitted through the same array antenna 2 as that in receiving similarly to the receive signal, and hence the transmitted radio signal is received by the portable telephone 4 of the user A as if the same has directivity for the user A. FIG. 19 is a diagram imaging such transfer of the radio signal between the user A and the adaptive array radio base station 1. In contrast with the area 3 of FIG. 16 showing the range where radio waves actually reach, such a state is imaged that the radio signal is flown from the adaptive array radio base station 1 with directivity while targeting the portable telephone 4 of the user A.
In order to implement such transfer of radio signals with directivity between a desired user and the adaptive array radio base station 1, it is necessary that the weights w1, w2, w3, . . . , wn are strictly calculated in the adaptive array radio base station 1 and weighting is equivalently performed on receive signals and transmit signals in the receiving part 1R and the transmission part 1T. However, even if control of weighting is completely performed, there is a case where transmission characteristics of the transmit signals change with respect to the receive signals and the transmit signals cannot be flown toward the target.
In the adaptive array radio base station 1 shown in FIG. 17, for example, the distances between the switches 10-1, 10-2, 10-3, . . . , 10-n and the corresponding multipliers 12-1, 12-2, 12-3, . . . , 12-n of the receiving part 1R and the distances between the switches 10-1, 10-2, 10-3, . . . , 10-n and the corresponding multipliers 15-1, 15-2, 15-3, . . . , 15-n of the transmission part 1T are not completely identical to each other in general. If there is difference between these distances, difference in quantity of phase rotation, difference in quantity of amplitude fluctuation and the like take place between the receive signal and the transmit signal received/transmitted in/from each antenna, and transmission/receiving of radio signals cannot be performed with excellent directivity between the targeted user and the adaptive array radio base station.
In particular, paths between the switches 10-1, 10-2, 10-3, . . . , 10-n and the corresponding multipliers of the receiving part 1R include necessary receiving circuits respectively and paths between these switches and the corresponding multipliers of the transmission part 1T include necessary transmission circuits respectively in general, although not shown in FIG. 17. These receiving circuits and transmission circuits are physically different circuits, and it follows that difference in quantity of phase rotation, difference in quantity of amplitude fluctuation and the like take place between the receive signal and the transmit signal received/transmitted in/from each antenna also depending on the characteristics of amplifiers, filters, mixers etc. forming these circuits. For example, it follows that phase rotation and amplitude fluctuation take place due to individual difference and temperature change etc. in the characteristics of an LNA (Low Noise Amplifier) included in the receiving circuit, an HPA (High Power Amplifier) included in the transmission circuit and the like.
In the adaptive array radio base station 1, therefore, it is necessary to calculate transmission characteristics such as the quantity of phase rotation and the quantity of amplitude fluctuation of the receiving circuit and transmission characteristics such as the quantity of phase rotation and the quantity of amplitude fluctuation of the transmission circuit for every antenna forming the array antenna 2 and correct the difference therebetween. A measuring circuit for measuring these transmission characteristics has been separately provided on the adaptive array radio base station in general, and hence there has been such a problem that the circuit structure of the adaptive array radio base station is enlarged and complicated and the cost also increases.
The present invention aims at providing a radio apparatus capable of calculating and correcting the difference in quantity of phase rotation and quantity of amplitude fluctuation of a receiving circuit and a transmission circuit with a simple and low-priced structure without providing a specific measuring circuit and a calibration method for its antenna directivity.